Stabilized aqueous gels and uses thereof

Claim 1

In a method wherein a fluid medium is introduced into a borehole in the earth and into contact with a subterranean formation penetrated by said borehole, the improvement wherein at least a portion of said fluid medium comprises an aqueous gel, and wherein said gel comprises an aqueous brine having incorporated therein: a water-thickening amount of a water-soluble cellulose ether; a water-soluble compound of a polyvalent metal, wherein said compound of a polyvalent metal is a compound of chromium or manganese wherein the valence of the chromium therein is +6 and the valence of at least a portion of said chromium is reduced to +3 and wherein the valence of the manganese therein is +7 and the valence of at least a portion of said manganese is reduced to +4, in an amount which is sufficient to cause gelation of said aqueous brine containing said cellulose ether when the valence of at least a portion of said metal is reduced to said lower valence state; a water-soluble reducing agent in an amount which is effective to reduce at least a portion of said metal to said lower valence state and cause said gelation with the formation of said gel wherein said reducing agent is selected from the group consisting of sodium or potassium sulfite, sodium or potassium hydrosulfite, sodium or potassium metabisulfite, sodium or potassium bisulfite, sodium or potassium sulfide, sodium or potassium thiosulfate, hydrogen sulfide, thioacetamide, hydroquinone, p-hydrazinobenzoic acid, hydrazine phosphite, hydrazine dichloride, and mixtures thereof; a water-soluble sulfoalkylated tannin capable of, and in an amount sufficient for, increasing the stability of said gel to decomposition, with said amount being sufficient to provide a weight ratio of the amount of said sulfoalkylated tannin to the amount of said polyvalent metal compound which is effective to cause said sulfoalkylated tannin to be effective in increasing the stability of said gel wherein the tannin molecule in said sulfoalkylated tannin is alkylated with a significant amount of --C(R) 2 --SO 3 M side chains wherein each R is selected from the group consisting of hydrogen and alkyl radicals containing from 1 to 5 carbon atoms, and M is selected from the group consisting of ammonium and the alkali metals, and said tannin is selected from the group consisting of the gallotannins and the flavotannins; wherein said amount of said cellulose ether is sufficient to provide a weight ratio of the amount of said cellulose ether to the amount of said polyvalent metal compound which is also effective to cause said sulfoalkylated tannin to be effective in increasing the stability of said gel, and wherein said weight ratio of the amount of said sulfoalkylated tannin to the amount of said polyvalent metal compound is within the range of from about 6.5:1 to about 27.5:1 and wherein said weight ratio of the amount of said cellulose ether to the amount of said polyvalent metal compound is at least about 20:1.